vSphere Storage I/O Control extends the constructs
of shares and limits to storage I/O resources. You can control the amount of
storage I/O that is allocated to virtual machines during periods of I/O
congestion, so that more important virtual machines get preference over less
important virtual machines for I/O resource allocation.

When vSphere Storage I/O Control is enabled on a
datastore, the ESXi host monitors the device latency when communicating with
that datastore. When device latency exceeds a threshold, the datastore is
considered to be congested and each virtual machine that accesses that
datastore is allocated I/O resources in proportion to their shares. Shares are
set on a per-virtual machine basis and can be adjusted.

vSphere Storage I/O Control has several
requirements, limitations, and constraints.

■

Datastores that are enabled with vSphere
Storage I/O Control must be managed by a single vCenter Server system.

■

Storage I/O Control is supported on Fibre
Channel-connected, iSCSI-connected, and NFS-connected storage. RDM is not
supported.

■

Storage I/O Control does not support datastores
with multiple extents.

■

Before using vSphere Storage I/O Control on
datastores that are backed by arrays with automated storage tiering
capabilities, check the
VMware Compatibility
Guide whether the storage array has been certified a compatible with
vSphere Storage I/O Control.

Storage I/O Control Design Decisions

Decision ID

Design Decision

Design Justification

Design Implication

SDDC-VI-Storage-005

Enable Storage I/O
Control with the default values on all non vSAN datastores.

Storage I/O Control ensures
that all virtual machines on a datastore receive an equal amount of I/O.

Virtual machines that use
more I/O are throttled to allow other virtual machines access to the datastore
only when contention occurs on the datastore.